pinctrl: sh-pfc: r8a7796: Add R8A77961 PFC support

Add support for the Pin Function Controller in the R-Car M3-W+
(R8A77961) SoC.

R-Car M3-W+ is pin compatible with R-Car M3-W (R8A77960), which allows
for both SoCs to share a driver.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Tested-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/20191023122955.12420-4-geert+renesas@glider.be